1. Field of the Invention
The present invention relates to a fixed-bed type catalytic reactor, particularly, to an improvement in gas-mixing apparatus in the reactor for catalytic reaction of gases.
2. State of the Art
In some chemical processes in which a catalytic reaction in gas-phase occurs by letting a reactant gas pass through two to three or more catalyst beds disposed in series along the direction of the gas flow in a reactor vessel, it is often required to mix a gas or gas-mixture which passed through a certain catalyst bed (hereinafter referred to as "the first gas") with another gas or gas-mixture (hereinafter referred to as "the second gas") before introducing them into the next catalyst bed. Such processes may include the process for producing styrene by catalytic dehydrogenation of ethylbenzene, for example. Because the dehydrogenation reaction is endothermic, the gas temperature in the catalyst bed decreases as the gas passes through the catalyst bed, and hence, the dehydrogenation reaction does no longer proceed at a satisfactory rate in the next catalyst bed. Thus, it is necessary to blow high temperature steam as a heat source into the effluent gas from a catalyst bed to increase the gas temperature therein.
In order to achieve uniform progress of the reaction and a high conversion, it is desired that the steam blown in between the catalyst beds is mixed with the reactant gas to the highest extent of homogeneity. On the other hand, the reactor is preferably small, and therefore, it is desirable that the space between the catalyst beds, which is available for mixing of the first gas and the second gas, should be as small as possible.
To date, there has been made some efforts to harmonize the above desires. One example is blowing of the second gas in radial or centripetal directions into the first gas flowing in the direction of axis of the reactor, and another is simultaneous blowing out of the first and the second gas from nozzles provided in a double tube so as to mix the gases at the time of blowing. These methods are still dissatisfactory because of insufficient homogeneity of mixing or complexity of structure of the mixing apparatus resulting in disadvantages in construction and maintenance.